BALTZLEY, Michael/J; LOHMANN, Kenneth/J; Universiy of North Carolina at Chapel Hill; Universiy of North Carolina at Chapel Hill: Characterization and function of neurons homologous to the Pd5 mucociliary motor neurons in the mollusc Tritonia diomedea.

The Pedal 5 (Pd5) neurons in the nudibranch gastropod Tritonia diomedea have been studied extensively because they show an increase in action potential firing rates in response to rotations of Earth-strength magnetic fields. Further characterization of these cells suggests that the Pd5 neurons are probably not primary magnetoreceptors, but are instead part of the motor circuitry that controls mucociliary crawling during orientation behavior. The Pd5 neurons produce a class of peptides called TPeps which have a cilioexcitatory effect on Tritonia pedal cilia. Tritonia also have an extensive network of TPep-immunoreactive neurites at the pedal epithelium. The presence of TPep-immunoreactive neurites at the pedal epithelium appears to be conserved across the gastropods. Neurons homologous to the Tritonia Pd5 cells were identified in several nudibranch species that crawl using mucociliary propulsion. Determination of homology was based on size, location, TPep-immunoreactivity, and neuroanatomy. We recorded intracellularly from the Pd5 homologues while exposing the animals to noxious stimuli that cause the animals to increase their rate of crawling. We also recorded extracellularly from nerves containing neurites of the Pd5 homologues to determine whether the action potentials recorded in the Pd5 somas represented afferent or efferent information.